I have seen many people creating New PortTypes for every Port even if they are of the same data type.
So I am giving a simple correlation between OOPs Classes and Biztalk PortTypes.
Class (Similar To) PortTypes - Just defines Oneway or TwoWay
Instance (Similar To) Ports - Defines Send or Receive direction, Binding Type
Methods (Similar To) Operations - Defines the operation on the port,